Index table assembly

ABSTRACT

An index table assembly includes a rotary table, a frame separated from the rotary table in the direction of a rotational axis of the rotary table, a clamping device for bringing the rotary table into contact with the frame by moving the rotary table along the rotational axis, a first bearing disposed between the rotary table and the frame, and an urging device disposed between the first bearing and one of the rotary table and the frame and pressing the first bearing against the other one of the rotary table and the frame at least when the rotary table rotates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to index table assemblies.

2. Description of the Related Art

Index table assemblies including a clamping device for bringing a rotarytable into contact with a frame by moving the rotary table along arotational axis thereof are known in the art (refer to, for example,Japanese Examined Utility Model Registration Application Publication No.7-50133, FIG. 1 on page 4). In such an index table assembly, the rotarytable is pressed against the frame over the entire circumference thereofwhen it is clamped, so that the rotary table is prevented from beingtilted by an external force applied during workpiece processing.Accordingly, the workpiece-processing accuracy is maintained.

In an index table assembly shown in FIG. 9, a clamping device includes aplurality of hydraulic actuators arranged in a frame 1 along a circlecentered on a rotational axis 15 at a constant interval. Each of thehydraulic actuators includes a piston 35 projecting from the frame 1,the piston 35 being fitted in a groove with a T-shaped cross sectionformed in a rotary table 2 such that a flange of the piston 35 engageswith step in the groove. When the rotary table 2 is clamped, each of thepistons 35 receives hydraulic pressure and moves in a retractingdirection. Accordingly, the rotary table 2 is pressed against the frame1 by the flanges of the pistons 35 and comes into contact with the frame1 over the entire circumference thereof. When the rotary table 2 isunclamped, the hydraulic pressure is removed and the rotary table 2 isreleased from the frame 1 so that the rotary table 2 can rotate.

As described above, when the rotary table 2 is unclamped, the hydraulicpressure is removed and the rotary table 2 is released from the frame 1so that the rotary table 2 can rotate. However, since the rotary table 2receives the load of onboard components such as a workpiece, a processtable, and a jig, the rotary table 2 comes into contact with the frame 1due to the load of the onboard components and its own load and largerotational resistance is caused. Therefore, a large amount of power isrequired to rotate the rotary table 2. In addition, a driving device ofthe rotary table 2, that is, a divider is quickly worn and theworkpiece-processing accuracy is degraded. In particular, when, forexample, the workpiece is unevenly placed and the center of gravity ofthe onboard components is distant from the rotational axis 15, therotary table 2 is strongly pressed against the frame 1 in a local regionof the frame 1 and the rotational resistance greatly increases. Inaddition, since the rotary table 2 does not always rotate by one turn, aclamping surface 2 b of the rotary table 2 and a clamping surface 1 b ofthe frame 1 are greatly worn in a certain region. In such a case, theperpendicularity of the clamping surfaces 2 b and 1 b of the rotarytable 2 and the frame 1, respectively, relative to the rotational axis15 is degraded. If the perpendicularity of the clamping surfaces 2 b and1 b relative to the rotational axis 15 is degraded, the clampingsurfaces 2 b and 1 b cannot be in even contact with each other over theentire circumference when the rotary table 2 is clamped and there is arisk that a gap will be generated in a certain region. In addition, evenwhen the clamping surfaces 2 b and 1 b can be in contact with each otherover the entire circumference, the perpendicularity of aworkpiece-receiving surface of the rotary table 2 relative to therotational axis 15 is degraded and the workpiece-processing accuracy isreduced accordingly. When a gap is generated between the clampingsurfaces 2 b and 1 b, the clamping force is reduced and the rotary table2 is tilted due to the external force applied during processing.Accordingly, also in this case, the workpiece-processing accuracy isreduced.

Therefore, an index table assembly disclosed in the above-mentionedpublication includes elastically deformable rolling elements disposedbetween a rotating ring fixed to a rotary table and a frame. In thisindex table assembly, when the rotary table is clamped, the rotatingring is urged toward the frame, moves along the rotational axis whiledeforming the rolling elements, and is pressed against the frame. Whenthe rotary table is unclamped, the urging force applied to the rotatingring is removed so that the rotary table can rotate, and the rollingelements return to their original shapes to support the rotating ringabove the frame. Accordingly, the rotational resistance of the rotarytable is equal to the rolling resistance of the rolling elements, andtherefore the rotary table can easily rotate.

However, when the rotary table rotates, the rolling elements receive notonly the load of the rotary table but also the load of onboardcomponents such a workpiece, a process table, and a jig, and aretherefore elastically deformed into a shape with an elliptical crosssection. Accordingly, the rolling elements are constantly deformed intoa shape with an elliptical cross section while they roll between therotating ring and the frame. Since a large force is required fordeforming the elastic elements, a large force is required for rollingthe rolling elements. Therefore, the rotational resistance of the rotarytable is also large in this index table assembly. In addition, since alarge force is required for rolling the rolling elements while deformingthem, sliding of the rolling elements relative to the rotating ring andthe frame occurs. Accordingly, the rolling elements are unevenly wornwith time and become harder to roll, which increases the degree ofsliding of the rolling elements relative to the rotating ring and theframe. As a result, the rolling elements are quickly worn and therotating ring comes into contact with the frame. Accordingly, therotational resistance of the rotary table increases and the rotatingring and the frame are worn, which leads to a reduction in theworkpiece-processing accuracy.

SUMMARY OF THE INVENTION

In order to solve the above-described problems, an object of the presentinvention is to provide an index table assembly in which a rotary tablecan easily rotate and the rotary table and a frame are prevented frombeing worn by coming into contact with each other, thereby maintainingthe workpiece-processing accuracy.

In order to attain the above-described object, an index table assemblyaccording to the present invention includes a rotary table; a frameseparated from the rotary table in the direction of a rotational axis ofthe rotary table; a clamping device for bringing the rotary table intocontact with the frame by moving the rotary table along the rotationalaxis; a first bearing disposed between the rotary table and the frame;and an urging device disposed between the first bearing and one of therotary table and the frame and pressing the first bearing against theother one of the rotary table and the frame at least when the rotarytable rotates.

The rotary table receives the load of onboard components such as aworkpiece, a process table, and a jig and its own load. Therefore, inthe index table assembly including the clamping device for bringing therotary table into contact with the frame by moving the rotary tablealong the rotational axis, there is a risk that the rotary table willcome into contact with the frame due to these loads when the rotarytable is unclamped from the clamping device. In such a case, rotationalresistance of the rotary table is caused. However, according to thepresent invention, the urging device is disposed between the firstbearing and one of the rotary table and the frame and presses the firstbearing against the other one of the rotary table and the frame at leastwhen the rotary table rotates. Therefore, the rotary table and the frameare prevented from coming into contact with each other due to the loadsand rotational resistance of the rotary table is not caused by contactbetween the rotary table and the frame. In addition, since the urgingdevice presses the first bearing against the other one of the rotarytable and the frame by pressing, that is, since the urging devicepresses the other one of the rotary table and the frame by pressing withthe first bearing, rotational resistance is not caused when the urgingdevice and the other one of the rotary table and the frame rotaterelative to each other. Therefore, rotational resistance of the rotarytable is not caused by the urging device.

Accordingly, the rotary table can easily rotate with low rotationalresistance, so that the energy is saved and an indexing speed isincreased. In addition, the rotary table, the frame, and a drivingdevice for the rotary table are prevented from being worn and theworkpiece-processing accuracy is maintained.

In the index table assembly according to the present invention, theurging device may include a plurality of springs arranged along a circlecentered on the rotational axis of the rotary table and the clampingdevice may bring the rotary table into contact with the frame against anurging force.

In such a case, since no dynamic power is used in the urging device, thestructure of the urging device is simplified and the clamping device canclamp the rotary table.

In addition, in the index table assembly according to the presentinvention, the urging device may include a hydraulic actuator which isnot activated when the rotary table is clamped.

In such a case, since the hydraulic actuator is not activated and theurging force applied by the urging device is removed when the rotarytable is clamped, the clamping device can clamp the rotary table bybringing the rotary table into contact with the frame without beingimpeded by the urging device.

In addition, in the index table assembly according to the presentinvention, the index table assembly may further include a second bearingdisposed between a surface of the rotary table on a side opposite to theside on which the first bearing and the urging device are provided andthe frame facing the surface, and the urging device may press the rotarytable against the second bearing at least when the rotary table rotates.

Accordingly, when the rotary table rotates, it is pressed against thesecond bearing and the second bearing is pressed against the frame bythe rotary table. Accordingly, the rotary table is restrained from beingmoved along the rotational axis by the urging device and is positionedrelative to the frame in the direction of the rotational axis withoutcausing rotational resistance. Since the urging device presses the firstbearing with a sufficient urging force while the rotary table rotates,the rotary table is prevented from being tilted.

In addition, in the index table assembly according to the presentinvention, the urging device may press the first bearing against theother one of the rotary table and the frame with an annular component.

In such a case, since the urging device presses the first bearing withthe annular component, the first bearing is uniformly pressed over theentire circumference thereof. Accordingly, the rotary table is preventedfrom being tilted and the rotary table and the frame are prevented fromcoming into contact with each other when the rotary table rotates.

In addition, in the index table assembly according to the presentinvention, the clamping device may include the annular component andpress the rotary table against the frame with the annular component, andthe urging device may be disposed between the first bearing and theframe and press the first bearing against the rotary table with theannular component.

In such a case, the urging device presses the first bearing against therotary table with the annular component, which is included in theclamping device. Accordingly, the overall structure of the index tableassembly is simplified.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional elevation view of an index table assemblyaccording to a first embodiment of the present invention taken alongline B-B in FIG. 2, which is a sectional plan view of the index tableassembly, in a state in which a rotary table is unclamped;

FIG. 2 is a sectional plan view of FIG. 1 taken along line A-A;

FIG. 3 is a sectional view of the main part of the index table assemblyaccording to the first embodiment of the present invention in a state inwhich the rotary table is clamped;

FIG. 4 is a sectional view of an index table assembly according to asecond embodiment of the present invention;

FIG. 5 is a sectional view of an index table assembly according to athird embodiment of the present invention;

FIG. 6 is a sectional view of an index table assembly according to afourth embodiment of the present invention;

FIG. 7 is a sectional view of the main part of a modification of theindex table assembly according to the fourth embodiment of the presentinvention;

FIG. 8 is a sectional view of an index table assembly according to afifth embodiment of the present invention; and

FIG. 9 is a sectional view of a known index table assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Embodiments of the present invention will be described below withreference to the accompanying drawings. FIGS. 1 and 2 are a sectionalelevation view and a sectional plan view, respectively, of an indextable assembly 100 according to a first embodiment of the presentinvention in a state in which a rotary table 2 is unclamped. Thesectional elevation view shown in FIG. 1 is taken along line B-B in FIG.2, and the sectional plan view shown in FIG. 2 is taken along line A-Ain FIG. 1. FIG. 3 is a sectional view showing the main part of the indextable assembly 100 in a state in which the rotary table 2 is clamped.

The index table assembly 100 includes the rotary table 2, a frame 1which supports the rotary table 2 such that the rotary table 2 canrotate, a worm wheel 4 fixed to the rotary table 2 with bolts (notshown), a worm 3 supported in the frame 1 by two tapered roller bearings21 and a radial bearing 20 interposed between the worm 3 and the frame1, and a drive motor 5 connected to the worm 3 with a coupling 6.

The rotary table 2 has a workpiece-receiving surface 2 a which isperpendicular to a rotational axis 15 and to which a process table, ajig, and the like (not shown) are attached and a clamping surface 2 b.The clamping surface 2 b is on the side opposite to theworkpiece-receiving surface 2 a, and is also perpendicular to therotational axis 15. In addition, a cover 13 is attached to the rotarytable 2 with bolts 25 to prevent foreign bodies such as cutting chipsand cutting fluid from entering the inside of the index table assembly100.

The frame 1 has a base surface 1 c which is fixed to a table surface ofa machine tool (not shown) and a clamping surface 1 b. The clampingsurface 1 b is on the side opposite to the base surface 1 c, and isperpendicular to the rotational axis 15. In addition, the clampingsurface 1 b faces the clamping surface 2 b of the rotary table 2.

In addition, the frame 1 includes a shaft portion 1 a centered on therotational axis 15 at the central region of the frame 1, and a radialroller bearing 11 is provided on the shaft portion 1 a. An inner race ofthe radial roller bearing 11 is fitted around the shaft portion 1 a andan outer race of the radial roller bearing 11 is fitted to the rotarytable 2, so that the rotary table 2 is rotatably supported by the radialroller bearing 11. The inner race of the radial roller bearing 11 isfixed to the shaft portion 1 a with distance rings 26 and 27 and abearing holder 14, which is detachably fixed to the shaft portion 1 awith bolts 22 at an end of the shaft portion 1 a.

A clamping device 105 includes a fluid path 1 d formed in the frame 1and connected to a pressure fluid source (not shown), an annularcylinder 16 fixed to the frame 1 with bolts 23 and having a fluid path16 a communicating with the fluid path 1 d, an annular piston 17 whichis slidable along the rotational axis 15 while being guided by the outerperipheral surface of the cylinder 16, and a clamp ring 18 fixed to therotary table 2 with bolts 24. A fluid pressure chamber 19 is providedbetween the outer peripheral surface of the cylinder 16 and the innerperipheral surface of the piston 17, and the fluid path 16 a opens tothe fluid pressure chamber 19 at one end thereof. Accordingly, the fluidpressure chamber 19 communicates with the fluid pressure source via thefluid paths 16 a and 1 d.

A surface of the rotary table 2 on the side opposite to theworkpiece-receiving surface 2 a is separated from the frame 1 in thedirection of the rotational axis 15, and an urging device 106 and athrust needle bearing 9, which serves as a first bearing, are disposedbetween them. The urging device 106 includes a plurality of compressioncoil springs 28 inserted in spring holes formed in the frame 1 along acircle centered on the rotational axis 15 at a constant interval. Thecompression coil springs 28 are in contact with the piston 17 whileapplying an urging force to the piston 17, and thereby press the thrustneedle bearing 9 against the rotary table 2 with the piston 17, whichserves as an annular component, interposed therebetween.

The rotary table 2 further has a surface on the side opposite to theside on which the thrust needle bearing 9 and the urging device 106 areprovided, that is, on the same side as the workpiece-receiving surface 2a, and a thrust ball bearing 10, which serves as a second bearing, isplaced between this surface and the bearing holder 14, that is, betweenthis surface and the frame 1.

Processes of clamping and unclamping the rotary table 2 by the clampingdevice 105 will be described below.

As shown in FIG. 3, when the rotary table 2 is clamped, pressure fluidis supplied to the fluid pressure chamber 19 from the pressure fluidsource via the fluid paths 1 d and 16 a, and the piston 17 moves towardthe base surface 1 c along the rotational axis 15 against the urgingforce applied by the compression coil springs 28. Accordingly, the clampring 18 engaging with the piston 17 moves together with the piston 17,and the rotary table 2 also moves toward the base surface 1 c until theclamping surface 2 b of the rotary table 2 and the clamping surface 1 bof the frame 1 come into contact with each other. When the clampingsurfaces 2 b and 1 b come into contact with each other, a frictionalforce is generated between them. Accordingly, the rotary table 2 isfixed to the frame 1 by the frictional force and is clamped such that itcannot rotate.

As shown in FIG. 1, when the rotary table 2 is unclamped, the pressureof the pressure fluid is reduced and the clamping surfaces 1 b and 2 bare released from each other. Accordingly, the rotary table 2 isunclamped such that it can rotate.

When the rotary table 2 is unclamped, it is supported by the thrustneedle bearing 9 and the thrust ball bearing 10 as described below andcan easily rotate with low rotational resistance.

The compression coil springs 28 are preferably designed by taking intoaccount the load of onboard components such as a workpiece, a processtable, and a jig and the load of the rotary table 2. In the presentembodiment, the compression coil springs 28 generate an urging forcesufficiently larger than the above-described loads placed thereon viathe rotary table 2. Accordingly, when the pressure of the pressure fluidis reduced, the compression coil springs 28 press the piston 17, and thepiston 17 presses the thrust needle bearing 9 against the rotary table2. Thus, the piston 17, the thrust needle bearing 9, and the rotarytable 2 move away from the base surface 1 c, and the clamping surface 2b is separated from the clamping surface 1 b.

When the rotary table 2 moves away from the base surface 1 c, it pressesthe thrust ball bearing 10 provided as the second bearing. Morespecifically, the rotary table 2 presses the thrust ball bearing 10against the bearing holder 14, that is, against the frame 1, so that therotary table 2 is positioned relative to the frame 1 in the direction ofthe rotational axis 15. In this state, the clamping surface 2 b and theclamping surface 1 b face each other with a predetermined gap providedtherebetween.

While the clamping surface 2 b and the clamping surface 1 b face eachother with a predetermined gap provided therebetween, the compressioncoil springs 28 continuously generate an urging force sufficientlylarger than the load of the onboard components such as a workpiece, aprocess table, and a jig and the load of the rotary table 2. Therefore,the rotary table 2 is prevented from being tilted due to these loads,particularly when the loads are placed unevenly. Accordingly, rotationalresistance is not caused by contact between the clamping surface 2 b andthe clamping surface 1 b.

In addition, although the rotary table 2 presses the bearing holder 14,that is, the frame 1 for positioning itself relative to the frame 1 inthe direction of the rotational axis 15, the rotary table 2 presses thebearing holder 14 with the thrust ball bearing 10 interposedtherebetween. Therefore, rotational resistance is not applied to therotary table 2 by frictional force generated between the rotary table 2and the frame 1.

As described above, in the index table assembly 100 according to thepresent embodiment, the rotary table 2 is prevented from coming intocontact with the frame 1 at least when it rotates, that is, when it isunclamped in the present embodiment, so that rotational resistance ofthe rotary table 2 is not caused and the clamping surfaces 1 b and 2 bare prevented from being worn. In addition, since the bearings, that is,the thrust needle bearing 9 and the thrust ball bearing 10 are placedbetween the rotary table 2 and the frame 1, rotational resistance is notcaused by engaging between the rotary table 2 and the frame 1 when therotary table 2 is unclamped.

Second Embodiment

FIG. 4 shows an index table assembly 110 according to a secondembodiment of the present invention in a state in which a rotary table 2is unclamped.

The rotary table 2 includes a bearing support 60 and a workpiecereceiver 61, and the bearing support 60 and the workpiece receiver 61are fixed to each other with bolts 8. The workpiece receiver 61 has aworkpiece-receiving surface 61 a and a clamping surface 61 b.

A clamping device 115 includes an annular piston 17 and a frame 1 havinga fluid path 1 d connected to a pressure fluid source and a slidingsurface along which the piston 17 slides on the inner periphery of theframe 1. A fluid pressure chamber 19 is formed between the innerperipheral surface of the frame 1 and the outer peripheral surface ofthe piston 17, and the fluid path 1 d opens to the fluid pressurechamber 19 at one end thereof. Accordingly, the fluid pressure chamber19 communicates with the fluid pressure source via the fluid path 1 d.

A surface of the rotary table 2 on the same side as theworkpiece-receiving surface 61 a is separated from the frame 1 in thedirection of the rotational axis 15, and an urging device 116 and athrust needle bearing 9, which serves as a first bearing, are disposedbetween them. The urging device 116 includes a plurality of compressioncoil springs 28 inserted in spring holes formed in a spring base 29,which is fixed to the frame 1 with bolts 57, along a circle centered onthe rotational axis 15 at a constant interval. The compression coilsprings 28 are in contact with the piston 17 while applying an urgingforce to the piston 17, and thereby press the thrust needle bearing 9against the rotary table 2 with the piston 17, which serves as anannular component, interposed therebetween.

The rotary table 2 further has a surface on the side opposite to theside on which the thrust needle bearing 9 and the urging device 116 areprovided, that is, on the side opposite to the workpiece-receivingsurface 61 a, and a thrust ball bearing 10, which serves as a secondbearing, is placed between this surface and the frame 1.

Processes of clamping and unclamping the rotary table 2 by the clampingdevice 115 are performed similar to the first embodiment. Morespecifically, the piston 17 moves toward the workpiece-receiving surface61 a along the rotational axis 15 against the urging force applied bythe compression coil springs 28. Accordingly, the rotary table 2, whichengages with the piston 17, moves away from a base surface 1 c until theclamping surface 61 b of the rotary table 2 and a clamping surface 29 aof the spring base 29 come into contact with each other. Thus, therotary table 2 is fixed to the frame 1 by a frictional force and isclamped such that it cannot rotate.

When the rotary table 2 is unclamped, it is released such that it canrotate, and is supported by the thrust needle bearing 9 and the thrustball bearing 10 such that it can easily rotate with low rotationalresistance. In addition, similar to the first embodiment, the rotarytable 2 is positioned in the direction of the rotational axis 15 by thethrust ball bearing 10 such that the clamping surfaces 61 b and 29 aface each other with a predetermined gap provided therebetween.

When the pressure of the pressure fluid is reduced, the compression coilsprings 28 press the piston 17, and the piston 17 presses the thrustneedle bearing 9 against the rotary table 2. Thus, the piston 17, thethrust needle bearing 9, and the rotary table 2 move toward the basesurface 1 c, and the clamping surface 61 b is separated from theclamping surface 29 a.

When the rotary table 2 moves toward the base surface 1 c, it pressesthe thrust ball bearing 10, which is provided as the second bearing.More specifically, the rotary table 2 presses the thrust ball bearing 10against the frame 1, so that the rotary table 2 is positioned relativeto the frame 1 in the direction of the rotational axis 15. In thisstate, the clamping surface 61 b and the clamping surface 29 a face eachother with a predetermined gap provided therebetween.

Similar to the index table assembly 100 according to the firstembodiment, in the index table assembly 110 according to the secondembodiment, the rotary table 2 is prevented from coming into contactwith the frame 1 at least when it rotates, that is, when it is unclampedin the present embodiment, so that rotational resistance of the rotarytable 2 is not caused and the clamping surfaces 29 a and 61 b areprevented from being worn. In addition, since the bearings, that is, thethrust needle bearing 9 and the thrust ball bearing 10 are placedbetween the rotary table 2 and the frame 1, rotational resistance is notcaused by engaging between the rotary table 2 and the frame 1.

Third Embodiment

FIG. 5 shows an index table assembly 120 according to a third embodimentof the present invention in a state in which a rotary table 2 isunclamped.

In the index table assembly 100 according to the first embodiment, theurging device 106 includes a plurality of springs. In comparison, anurging device 126 of the index table assembly 120 includes a hydraulicactuator. In addition, different from the index table assembly 100 inwhich the thrust ball bearing 10 is provided as the second bearing, theindex table assembly 120 includes a tapered roller bearing 32 as asecond bearing. The tapered roller bearing 32 serves the functions ofboth a radial bearing and a thrust bearing.

A frame 1 includes a shaft portion 1 a centered on a rotational axis 15at the central region of the frame 1, and the tapered roller bearing 32is provided on the shaft portion 1 a. An inner race of the taperedroller bearing 32 is fitted around the shaft portion 1 a and an outerrace of the tapered roller bearing 32 is fitted to the rotary table 2,so that the rotary table 2 is rotatably supported by the tapered rollerbearing 32. The inner race of the tapered roller bearing 32 is fixed tothe shaft portion 1 a with a distance ring 34 and a nut 33 which isscrewed on a male thread formed in the shaft portion 1 a at an endthereof.

A clamping device 125 is identical to the clamping device 105 includedin the index table assembly 100 according to the first embodiment isprovided. Similar to the clamping device 105, the rotary table 2 isclamped by bringing a clamping surface 2 b of the rotary table 2 and aclamping surface 1 b of the frame 1 into contact with each other.

A surface of the rotary table 2 on the side opposite to aworkpiece-receiving surface 2 a is separated from the frame 1 in thedirection of a rotational axis 15, and the urging device 126 and athrust needle bearing 9, which serves as a first bearing, are disposedbetween them. The urging device 126 includes a piston 17 and a cylinder16 included in the clamping device 125, the frame 1, and a fluid path 1e formed in the frame 1 and connected to a pressure fluid source (notshown). A fluid pressure chamber 31 for urging is provided between theouter peripheral surface of the cylinder 16 and the inner peripheralsurface of the frame 1, and the fluid path 1 e opens to the fluidpressure chamber 31 at one end thereof. Accordingly, the fluid pressurechamber 31 communicates with the fluid pressure source via the fluidpath 1 e.

When the rotary table 2 is unclamped, a switching valve (not shown)changes the flow path to which pressure fluid from the pressure fluidsource is supplied from a fluid path 1 d to the fluid path 1 e.Accordingly, the pressure of the pressure fluid in a fluid pressurechamber 30 is reduced and the rotary table 2 is unclamped. In addition,the pressure fluid flows into the fluid pressure chamber 31 and movesthe piston 17 toward the workpiece-receiving surface 2 a. The piston 17presses the thrust needle bearing 9 against the rotary table 2, and therotary table 2 presses the outer race of the tapered roller bearing 32.The outer race of the tapered roller bearing 32 presses rolling elementswhich are restrained from moving along the rotational axis 15 by theinner race. Accordingly, the rotary table 2 is positioned in thedirection of the rotational axis 15, and the clamping surfaces 2 b and 1b face each other with a predetermined gap provided therebetween.

According to the present embodiment, when the rotary table 2 isunclamped, the switching valve changes the flow path to which thepressure fluid from the pressure fluid source is supplied from the fluidpath 1 d to the fluid path 1 e. However, supply of the pressure fluidmay also be stopped when the rotary table 2 is unclamped. In such acase, the pressure fluid is supplied to the fluid path 1 e when therotary table 2 rotates.

Similar to the index table assembly 100, the rotary table 2 is preventedfrom coming into contact with the frame 1 at least when it rotates, sothat rotational resistance of the rotary table 2 is not caused and theclamping surfaces 1 b and 2 b are prevented from being worn. Inaddition, since the bearings, that is, the thrust needle bearing 9 andthe tapered roller bearing 32 are placed between the rotary table 2 andthe frame 1, rotational resistance is not caused by engaging between therotary table 2 and the frame 1.

Fourth Embodiment

FIG. 6 shows an index table assembly 130 according to a fourthembodiment of the present invention in a state in which a rotary table 2is unclamped.

Similar to the index table assembly 100 according to the firstembodiment, a frame 1 includes a shaft portion 1 a centered on arotational axis 15 at the central region of the frame 1, and a radialroller bearing 11 is provided on the shaft portion 1 a. An inner race ofthe radial roller bearing 11 is fitted around the shaft portion 1 a andan outer race of the radial roller bearing 11 is fitted to the rotarytable 2, so that the rotary table 2 is rotatably supported by the radialroller bearing 11. The inner race of the radial roller bearing 11 isfixed to the shaft portion 1 a with distance rings 26 and 27 and abearing holder 14 which is detachably fixed to the shaft portion 1 awith bolts 22 at an end of the shaft portion 1 a.

A clamping device 135 includes a fluid path 1 d formed in the frame 1and connected to a pressure fluid source (not shown); a plurality ofcylinder holes 1 h formed in the frame 1 along a circle centered on therotational axis 15 at a constant interval; pistons 35 inserted in thecylinder holes 1 h and having flanges at an end thereof; piston holders36 fixed to the frame 1 with bolts 43 and inserted into the cylinderholes 1 h; a piston groove 37 with a T-shaped cross section formed inthe rotary table 2 along a circle centered on the rotational axis 15over the entire circumference thereof such that the piston groove 37opens in a clamping surface 2 b, the piston groove 37 accommodating theflanges of the pistons 35; and compression coil springs 45 inserted inspring holes formed in the pistons 35 at the end opposite to theflanges. Fluid pressure chambers 39 are formed between the cylinderholes 1 h and the pistons 35, and the fluid path 1 d opens to the fluidpressure chambers 39 at one end thereof. The compression coil springs 45are in contact with the frame 1 at one end thereof and urge the pistons35 toward a workpiece-receiving surface 2 a.

A surface of the rotary table 2 on the side opposite to theworkpiece-receiving surface 2 a is separated from the frame 1 in thedirection of the rotational axis 15, and an urging device 136, apressing ring 41, and a thrust ball bearing 40, which serves as a firstbearing, are disposed between them. The urging device 136 includes aplurality of compression coil springs 28 inserted in spring holes formedin the frame 1 along a circle centered on the rotational axis 15 at aconstant interval. The compression coil springs 28 are in contact withthe pressing ring 41 while applying an urging force to the pressing ring41, and thereby press the thrust ball bearing 40 against the rotarytable 2 with the pressing ring 41 interposed therebetween. In addition,a guide ring 42 is fixed to the frame 1 with bolts 44, and the pressingring 41 is guided by the guide ring 42.

Processes of clamping and unclamping the rotary table 2 by the clampingdevice 135 will be described below.

When the rotary table 2 is clamped, pressure fluid is supplied to thefluid pressure chambers 39 from the pressure fluid source via the fluidpath 1 d, and the pistons 35 move toward a base surface 1 c along therotational axis 15 against the urging force applied by the compressioncoil springs 28 and 45. Accordingly, the rotary table 2, which isengaged with the pistons 35 by the piston groove 37, moves toward thebase surface 1 c until the clamping surface 2 b of the rotary table 2and a clamping surface 1 b of the frame 1 come into contact with eachother. When the clamping surfaces 2 b and 1 b come into contact witheach other, a frictional force is generated between them. Accordingly,the rotary table 2 is fixed to the frame 1 by the frictional force andis clamped such that it cannot rotate.

When the rotary table 2 is unclamped, the pressure of the pressure fluidis reduced and the pistons 35 are pressed against the rotary table 2 bythe urging force applied by the compression coil springs 45, so that theclamping surfaces 1 b and 2 b are released from each other. Accordingly,the rotary table 2 is unclamped such that it can rotate.

Similar to the index table assembly 100 according to the firstembodiment, when the rotary table 2 unclamped, it is supported by twothrust bearings, that is, the thrust ball bearing 40 and a thrust ballbearing 10 and can easily rotate with low rotational resistance.

When the pressure of the pressure fluid is reduced, the compression coilsprings 28 press the pressing ring 41, and the pressing ring 41 pressesthe thrust ball bearing 40 against the rotary table 2. Thus, thepressing ring 41, the thrust ball bearing 40, and the rotary table 2move away from the base surface 1 c, and the clamping surface 2 b isseparated from the clamping surface 1 b.

Similar to the index table assembly 100 according to the firstembodiment, the rotary table 2 presses the thrust ball bearing 10, whichis provided as a second bearing, so that the rotary table 2 ispositioned relative to the frame 1 in the direction of the rotationalaxis 15. In this state, the clamping surface 2 b and the clampingsurface 1 b face each other with a predetermined gap providedtherebetween.

Accordingly, similar to the index table assembly 100 according to thefirst embodiment, rotational resistance of the rotary table 2 is notcaused and the rotary table 2 and the frame 1 are prevented from beingworn by coming into contact with each other at least when the rotarytable 2 rotates, that is, when it is unclamped in the presentembodiment.

As shown in FIG. 7, a plurality of spring holes for receiving thecompression coil springs 28 may also be formed in the rotary table 2along a circle centered on the rotational axis 15 at a constantinterval. In such a case, the compression coil springs 28 press thethrust ball bearing 40 against the frame 1 with the pressing ring 41interposed therebetween. Also in this case, the clamping surfaces 1 band 2 b are separated from each other when the rotary table 2 isunclamped.

Fifth Embodiment

FIG. 8 shows an index table assembly 140 according to a fifth embodimentof the present invention in a state in which a rotary table 2 isunclamped.

A surface of the rotary table 2 on the side opposite to aworkpiece-receiving surface 2 a is separated from a frame 1 in thedirection of a rotational axis 15, and an urging device identical to theurging device 136 included in the index table assembly 130 according tothe fourth embodiment, a pressing ring 41, and a thrust ball bearing 40are disposed between them.

Two clamping devices 145 and 146 are provided, the clamping device 145being used for bringing the rotary table 2 into contact with the frame 1by moving the rotary table 2 along the rotational axis 15 and theclamping device 146 being used for bringing a component fixed to theframe 1 into contact with the rotary table 2 by deforming the component.

Similar to the index table assembly 120 according to the thirdembodiment, the frame 1 has a shaft portion 1 a centered on therotational axis 15 at the central region of the frame 1, and a taperedroller bearing 32 is provided on the shaft portion 1 a. An inner race ofthe tapered roller bearing 32 is fitted around the shaft portion 1 a andan outer race of the tapered roller bearing 32 is fitted to the rotarytable 2, so that the rotary table 2 is rotatably supported by thetapered roller bearing 32. The inner race of the tapered roller bearing32 is fixed to the shaft portion 1 a with a distance ring 34 and a nut33 which is screwed on a male thread formed in the shaft portion 1 a atan end thereof.

The frame 1 has a through hole centered on the rotational axis 15, and acenter shaft 48 fixed to the rotary table 2 with bolts 54 is insertedinto the through hole. In addition, the through hole is provided with acylinder in which a piston 50 is inserted. A fluid pressure chamber 51is formed in the cylinder, and a fluid path if formed in the frame 1 andconnected to a pressure fluid source opens to the fluid pressure chamber51. A piston holder 49 is fixed on an end surface of the center shaft 48with bolts 55 such that the piston holder 49 extends through a throughhole formed in the piston 50 and is engaged with the piston 50. Inaddition, a spring holder 52 having a plurality of spring holes arrangedalong a circle centered on the rotational axis 15 is fixed to the frame1 with bolts 56. The spring holes formed in the spring holder 52accommodate compression coil springs 45 which are in contact with thepiston 50 at one end thereof, and the compression coil springs 45 urgethe piston 50 toward the workpiece-receiving surface 2 a.

The clamping device 145 includes the cylinder formed in the through holeof the frame 1, the piston 50, the compression coil springs 45, thespring holder 52, the piston holder 49, and the fluid path 1 f. Whenpressure fluid is supplied to the fluid pressure chamber 51, the rotarytable 2 moves along the rotational axis 15 and comes into contact withthe frame 1.

A clamp ring 46 is fixed to the frame 1 with bolts 53. The clamp ring 46extends along the rotational axis 15, and the inner peripheral surfaceof the clamp ring 46 is fitted around a shaft portion 2 c of the rotarytable 2. In addition, the clamp ring 46 has a groove with a certainwidth along the rotational axis 15 in the outer peripheral surfacethereof, the groove extending over the entire circumference of the clampring 46. Accordingly, a fluid pressure chamber 47 is formed between theclamp ring 46 and the frame 1 such that a thin portion of the clamp ring46 is provided between the fluid pressure chamber 47 and the shaftportion 2 c. The frame 1 has a fluid path 1 g connected to the pressurefluid source, and the fluid path 1 g opens to the fluid pressure chamber47 at one end thereof.

The clamping device 146 includes the clamp ring 46 and the fluid path 1g. When the pressure fluid is supplied to the fluid pressure chamber 47,the thin portion of the clamp ring 46 fixed to the frame 1 is deformedand comes into contact with the rotary table 2.

Processes of clamping and unclamping the rotary table 2 by the twoclamping devices 145 and 146 will be described below.

When the rotary table 2 is clamped, the pressure fluid is supplied tothe fluid path 1 f, and the piston 50 moves toward a base surface 1 c ofthe frame 1 against the urging force applied by the compression coilsprings 28 and 45 and press the piston holder 49, which is engaged withthe piston 50. Accordingly, the piston holder 49 and the rotary table 2moves together until a clamping surface 1 b of the frame 1 and aclamping surface 2 b of the rotary table 2 come into contact with eachother. Thus, the rotary table 2 is clamped. Next, the pressure fluid issupplied to the fluid path 1 g so that it flows into the fluid pressurechamber 47. Accordingly, the thin portion of the clamp ring 46 isdeformed such that it swells inward and comes into contact with theshaft portion 2 c of the rotary table 2. Thus, the clamp ring 46, whichis fixed to the frame 1, comes into contact with the rotary table 2 andthe rotary table 2 is strongly clamped.

When the rotary table 2 is unclamped, the pressure of the pressure fluidis reduced, so that the clamping surfaces 1 b and 2 b are released fromeach other and the thin portion of the clamp ring 46 and the shaftportion 2 c of the rotary table 2 are also released from each other.Accordingly, the rotary table 2 is unclamped such that it can rotate.

When the pressure of the pressure fluid is reduced, the compression coilsprings 28 press the pressing ring 41, and the pressing ring 41 pressesthe thrust ball bearing 40 against the rotary table 2. Accordingly, therotary table 2 presses the outer race of the tapered roller bearing 32.The outer race of the tapered roller bearing 32 presses rolling elementswhich are restrained from moving along the rotational axis 15 by theinner race. Accordingly, the rotary table 2 is positioned in thedirection of the rotational axis 15, and the clamping surfaces 2 b and 1b face each other with a predetermined gap provided therebetween.

As in the modification of the index table assembly 130 according to thefourth embodiment shown in FIG. 7, a plurality of spring holes forreceiving the compression coil springs 28 may also be formed in therotary table 2 along a circle centered on the rotational axis 15 at aconstant interval. In such a case, the compression coil springs 28presses the thrust ball bearing 40 against the frame 1 with the pressingring 41 interposed therebetween. Also in this case, the clampingsurfaces 1 b and 2 b are separated from each other when the rotary table2 is unclamped.

The present invention is not limited to the above-described embodiments,and various modifications are possible within the scope of the presentinvention.

1. An index table assembly comprising: a rotary table having aworkpiece-receiving surface (2 a) receiving the load of onboardcomponents such as a workpiece; a frame separated from the rotary tablein the direction of a rotational axis of the rotary table; a clampingdevice for causing rotational resistance of the rotary table by bringingthe clamping surface of rotary table on the side opposite to theworkpiece-receiving surface into contact with the frame by moving therotary table together with the workpiece-receiving surface along therotational axis, wherein the rotational resistance is caused by clampingthe rotary table against the frame such that the rotary table cannotrotate; a first bearing disposed between the rotary table and the frame;an urging device disposed between the first bearing and the frame suchthat said urging device is in contact with the first bearing and theframe, and pressing the first bearing against the rotary table at leastwhen the rotary table rotates; and a second bearing disposed between asurface of the rotary table and a surface of the frame facing thesurface of the rotary table, said second bearing in contact with bothsaid surfaces thereof, wherein the urging device presses the rotarytable against the second bearing at least when the rotary table rotates.2. An index table assembly according to claim 1, wherein the urgingdevice comprises a plurality of springs arranged along a circle centeredon the rotational axis of the rotary table and the clamping devicebrings the rotary table into contact with the frame against an urgingforce.
 3. An index table assembly according to claim 1, wherein theurging device presses the first bearing against the rotary, and whereinthe urging device contacts the first bearing with an urging force whichcomprises an annular component which can move in the direction of therotational axis of the rotating table in the frame.
 4. An index tableassembly according to claim 3, wherein the clamping device includes theannular component and presses the rotary table against the frame withthe annular component, and the urging device is disposed between thefirst bearing and the frame and presses the first bearing against therotary table with the annular component.